Exhaust gas purification apparatus of internal combustion engine and catalyst for purifying exhaust gas internal combustion engine

• US 6,161,378 A
• Filed: 12/10/1998
• Issued: 12/19/2000
• Est. Priority Date: 06/10/1996
• Status: Expired due to Term

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Hitachi, Ltd.
• Inventors: Kuroda, Osamu, Ogawa, Toshio, Shinotsuka, Norihiro, Iizuka, Hidehiro, Yamashita, Hisao, Kitahara, Yuichi, Hiratsuka, Toshifumi, Okude, Kojiro, Manaka, Toshio, Doi, Ryouta, Azuhata, Shigeru, Hanaoka, Hiroshi
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/202,243
• Time in Patent Office: 740 Days
• Field of Search: 60/286, 60/303, 60/274, 60/295, 60/297, 60/301, 60/299, 422/169, 422/170, 422/171, 422/177
• US Class Current: 60/286
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 2255/2022 Potassium
• CPC Class Codes: B01D 2255/2027 Sodium
• CPC Class Codes: B01D 2255/2047 Magnesium
• CPC Class Codes: B01D 2255/2061 Yttrium
• CPC Class Codes: B01D 2255/2063 Lanthanum
• CPC Class Codes: B01D 2255/2065 Cerium
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 53/9422 for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2510/06 for exhaust purification, e.g. catalytic reaction
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 : Nitrogen oxides
• CPC Class Codes: F01N 3/0871 : Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/0878 : Bypassing absorbents or adsorbents
• CPC Class Codes: F02D 2200/0806 : NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 2200/0814 : Oxygen storage amount
• CPC Class Codes: F02D 41/027 : to purge or regenerate the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/0275 : the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1455 : with sensor resistivity varying with oxygen concentration F02D41/1456 takes precedence
• CPC Class Codes: F02D 41/146 : the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/1462 : with determination means using an estimation
• CPC Class Codes: F02D 41/1463 : of the exhaust gases downstream of exhaust gas treatment apparatus
• CPC Class Codes: F02D 41/1465 : with determination means using an estimation
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

An exhaust gas purification apparatus for use in an internal combustion engine comprises an exhaust gas duct connected to the engine through which exhaust gas containing NO_x gas passes, and a catalyst disposed in the exhaust gas duct such that it contacts the exhaust gas. The catalyst chemically adsorbs NO_x when a stoichiometric amount of a gaseous oxidizing agent present in the exhaust gas is larger than that of a gaseous reducing agent present in the exhaust gas for reducing NO_x, adsorbed NO_x is catalytically reduced in the presence of a reducing agent when the stoichiometric amount of the oxidizing agent is not larger that of the reducing agent.

Claims

1. A method of purifying an exhaust gas from an internal combustion engine having a lean operation mode, comprising:

providing a catalyst which both chemically adsorbs NO_x and reduces adsorbed NO_x when an amount of a gaseous reducing agent in said exhaust gas is less than stoichiometric with respect to an amount of a gaseous oxidizing agent in the exhaust gas, and which catalyzes a reduction of adsorbed NO_x when the amount of said reducing agent is equal to or more than stoichiometric with respect to the amount of said oxidizing agent in the exhaust gas;

passing said exhaust gas over said catalyst;

operating said engine in said lean combustion mode; and

intermittently controlling said amount of said reducing agent present in said exhaust gas to increase it to an amount which is greater than or equal to stoichiometric with respect to an amount of said oxidizing agent in said exhaust gas;

wherein said catalyst comprises at least one member selected from each of the following groups;

a first group consisting of alkali metals, calcium and strontium;

a second group consisting of rare earth metals;

a third group consisting of platinum group metals; and

a fourth group consisting of silicon and titanium.

2. Method according to claim 1 wherein said step of intermittently controlling comprises adding an amount of said reducing agent to said exhaust gas.

3. Method according to claim 1 wherein:

said step of intermittently controlling comprises switching said engine to a rich combustion mode.

4. An exhaust gas purification apparatus for an internal combustion engine having a lean operation mode with a lean air fuel ratio of at least 18, comprising:

an exhaust gas duct connected to said engine, through which the exhaust gas containing NOx passes; and

a main catalyst disposed in said exhaust gas duct, in contact with the exhaust gas;

wherein

said main catalyst chemically adsorbs and retains NOx on a surface portion thereof in the presence of said exhaust gas when said engine operates in said lean operation mode;

NOx retained on said main catalyst is reduced to N₂ in the presence of said exhaust gas when said engine operates with a rich or stoichiometric air fuel ratio and when said engine operates in said lean operation mode; and

said main catalyst comprises at least one member selected from each of the following groups;

a first group consisting of alkali metals, calcium and strontium;

a second group consisting of rare earth metals;

a third group consisting of platinum group metals; and

a fourth group consisting of silicon and titanium.

5. An exhaust gas purification apparatus according to claim 4 further comprising a timing control unit which outputs a timing signal to determine a period for operation of said engine with a rich or stoichiometric air/fuel ratio.

6. An exhaust gas purification apparatus according to claim 4 wherein said catalyst comprises:

a heat resistant carrier body; and

catalytic compounds supported on said carrier body.

7. An exhaust gas purification apparatus according to claim 4, further comprising a manifold catalyst disposed in said exhaust gas duct immediately after the engine, upstream of said main catalyst, said manifold catalyst having functions of a three way catalyst and a combustion catalyst.

8. An exhaust gas purification apparatus according to claim 7, wherein

said manifold catalyst is disposed in an exhaust gas duct of a direct fuel injection engine.

9. An exhaust gas purification apparatus according to claim 4, further comprising one of a three way catalyst and a combustion catalyst disposed in said exhaust gas duct at the upstream of said main catalyst.

10. The exhaust gas purification apparatus according to claim 4, further comprising a second catalyst disposed downstream of said main catalyst, for removing impurities from said exhaust gas.

11. The exhaust gas purification apparatus according to claim 10 wherein said impurities comprise at least one of hydrocarbons, carbon monoxide and NOx.

12. The exhaust gas purification apparatus according to claim 4 wherein NOx retained on said main catalyst is in the form of NO₂.

13. The exhaust gas purification apparatus according to claim 4 wherein said at least one member selected from said fourth group is titanium.

14. The exhaust gas purification apparatus according to claim 4 wherein said at least one member selected from said first group is at least one of sodium, potassium and lithium.

15. The exhaust gas purification apparatus according to claim 4 wherein said at least one member selected from said second group is cerium.

16. The exhaust gas purification apparatus according to claim 4 wherein said at least one member selected from said third group comprises platinum and rhodium.

17. The exhaust gas purification apparatus according to claim 4 wherein said at least one member selected from said first group is strontium.

18. The exhaust gas purification apparatus according to claim 4 wherein said main catalyst further comprises magnesium.

19. The exhaust gas purification apparatus according to claim 4, further comprising:

an engine control unit which estimates NOx accumulation during operation of said engine in said lean operation mode, based on detected vehicle operating parameters;

wherein said engine control unit switches said engine to operation with a rich or stoichiometric air fuel ratio when estimated accumulated NOx exceeds a preset value.

20. The exhaust gas purification apparatus according to claim 4, further comprising:

an oxygen sensor arranged in an exhaust gas flow of said engine; and

an engine control unit which determines an accumulated value of oxygen in said exhaust gas, based on an output signal of said oxygen sensor;

wherein said engine control unit switches said engine to operation with a rich or stoichiometric air/fuel ratio when said accumulated value exceeds a predetermined threshold value.

21. The exhaust gas purification apparatus according to claim 20, wherein determination of accumulated oxygen is performed only during operation of said engine in said lean operating mode.

22. The exhaust gas purification apparatus according to claim 20, wherein determination of accumulated oxygen is performed during all operation modes of said engine.

23. The exhaust gas purification apparatus according to claim 4, further comprising:

an NOx sensor disposed upstream of said main catalyst in a flow of said exhaust gas; and

an engine control unit determines an accumulated value of NOx in said exhaust gas, based on an output of said NOx sensor;

wherein said engine control unit switches said engine to operation with a rich or stoichiometric air/fuel ratio when said accumulated value exceeds a predetermined threshold value.

24. The exhaust gas purification apparatus according to claim 4, further comprising:

an NOx sensor disposed downstream of said main catalyst in a flow of said exhaust gas; and

an engine control unit determines an accumulated value of NOx in said exhaust gas, based on an output of said NOx sensor;

wherein said engine control unit switches said engine to operation with a rich or stoichiometric air/fuel ratio when said accumulated value exceeds a predetermined threshold value.

25. The exhaust gas purification apparatus according to claim 4, wherein said internal combustion is a gasoline engine.

26. An exhaust gas purification apparatus for an internal combustion engine having a lean operation mode with a lean air fuel ratio, comprising:

an exhaust gas duct connected to said engine, through which the exhaust gas containing NOx passes; and

a main catalyst disposed in said exhaust gas duct, in contact with the exhaust gas;

wherein

said main catalyst chemically adsorbs and retains NOx on a surface portion thereof in the presence of said exhaust gas when an amount of a reducing agent in said exhaust gas is less than stoichiometric with respect to an amount of oxidizing agent in said exhaust gas;

NOx retained on said main catalyst is reduced to N₂ in the presence of said exhaust gas when an amount of a reducing agent in said exhaust gas is equal to or more than stoichiometric with respect to an amount of oxidizing agent in said exhaust gas, and when said engine operates in said lean operation mode; and

said main catalyst comprises at least one member selected from each of the following groups;

a first group consisting of alkali metals, calcium and strontium;

a second group consisting of rare earth metals;

a third group consisting of platinum group metals; and

a fourth group consisting of silicon and titanium.

27. An exhaust gas purification apparatus according to claim 26 wherein

said reducing agent present in the lean combustion exhaust gas is at least one of gasoline, light oil, kerosene, natural gas, their reformed substances, hydrogen, alcohol, ammonia gas, engine blow by gas and canister purging gas.

28. An exhaust gas purification apparatus according to claim 26, further comprising a timing control unit, wherein said reducing agent is supplied to the lean combustion exhaust gas in response to signals from said timing control unit.

29. The apparatus for purifying an exhaust gas according to claim 26, wherein:

said main catalyst chemically adsorbs NO_x when the exhaust gas is emitted from lean combustion;

NO_x adsorbed by said catalyst is catalytically reduced when a gaseous reducing agent is added to the lean combustion exhaust gas; and

said catalyst adsorbs or absorbs SOx in a lean condition, and releases SOx in a stoichiometric or rich condition.